My Math Forum  

Go Back   My Math Forum > High School Math Forum > Algebra

Algebra Pre-Algebra and Basic Algebra Math Forum


Thanks Tree5Thanks
Reply
 
LinkBack Thread Tools Display Modes
March 18th, 2017, 09:19 PM   #1
Member
 
Joined: Jan 2017
From: US

Posts: 65
Thanks: 5

Algebra, and Graphing, and Functions, and...What??

So, how would you determine if f(x)=-x$\displaystyle ^2$-1 has a minimum or a maximum? And also, how would you go about graphing it?

Sorry if I seem ignorant on the subject; but hey, that's what math forums are for, right? Hehe

Thanks in advance!
Indigo28 is offline  
 
March 18th, 2017, 09:27 PM   #2
Senior Member
 
Joined: Feb 2016
From: Australia

Posts: 982
Thanks: 347

Math Focus: Yet to find out.
I think it may help ignore you start by drawing a rough graph to get a feel for the function, then proceed in finding its min/max. Do you know how to draw a graph of a function?
Thanks from Indigo28
Joppy is offline  
March 18th, 2017, 09:37 PM   #3
Member
 
Joined: Jan 2017
From: US

Posts: 65
Thanks: 5

Quote:
Originally Posted by Joppy View Post
I think it may help ignore you start by drawing a rough graph to get a feel for the function, then proceed in finding its min/max. Do you know how to draw a graph of a function?
I am going to be really honest, no I don't. But I would definitely be open to it if you could sum up how to graph a function. I am pretty new to the graphing thing, just getting into that in Algebra. So your help is definitely appreciated!
Indigo28 is offline  
March 19th, 2017, 12:23 AM   #4
Global Moderator
 
Joined: Dec 2006

Posts: 16,782
Thanks: 1238

Do you see why -x² - 1 can't be greater than -1 if x is real?
Thanks from Indigo28
skipjack is offline  
March 20th, 2017, 02:12 AM   #5
Newbie
 
Joined: Mar 2017
From: VietNam

Posts: 7
Thanks: 2

The easiest way is go to desmos.com and type the function!
When you look at the graph, you can see what is maximum or minimum (if they exist!)
For example, this function f(x)=-x^2-1 has vertex (0;-1), and looking at the graph we can see that it has one maximum = -1, and no minimum!
Thanks from Indigo28

Last edited by skipjack; March 20th, 2017 at 02:26 AM.
MathAssighmentTutor is offline  
March 21st, 2017, 02:56 PM   #6
Member
 
Joined: Jan 2017
From: US

Posts: 65
Thanks: 5

Quote:
Originally Posted by MathAssighmentTutor View Post
The easiest way is go to desmos.com and type the function!
When you look at the graph, you can see what is maximum or minimum (if they exist!)
For example, this function f(x)=-x^2-1 has vertex (0;-1), and looking at the graph we can see that it has one maximum = -1, and no minimum!
Thanks! I found this particularly helpful, because I use desmos a lot, for graphing and such. I wasn't sure what the maximum or minimum were before, but now that I know, I definitely think that will come in handy!
Indigo28 is offline  
March 21st, 2017, 04:46 PM   #7
Senior Member
 
Joined: Aug 2012

Posts: 1,152
Thanks: 252

Quote:
Originally Posted by Indigo28 View Post
Thanks! I found this particularly helpful, because I use desmos a lot, for graphing and such. I wasn't sure what the maximum or minimum were before, but now that I know, I definitely think that will come in handy!
As an oldtimer who learned algebra before they had computers (No! Was there ever such a time?) I wanted to suggest that you learn to do these by hand and not rely on the graphing calculator.

But then I thought ... is that true? If someone is learning algebra today, should they learn to make a two-column table, label the columns x and f(x), and plug in numbers by hand? Then plot the points (x, f(x)) on graph paper. This is how you get a visceral feel for the functions.

But I do wonder if that's true. I'd love to hear people's opinions about this. When we teach algebra in the modern world, should we make people graph points by hand and only use the calculator as a secondary tool? Or should i just forget about it, get off my dinosaur, and tell the kids, 'There's an app for that!"

OP what do you think? Do you understand that the points on the graph are exactly the points (x, f(x)) on the plane? That's the main thing to know.
Thanks from Indigo28
Maschke is offline  
March 21st, 2017, 05:10 PM   #8
Senior Member
 
Joined: May 2016
From: USA

Posts: 577
Thanks: 248

Quote:
Originally Posted by Maschke View Post
As an oldtimer who learned algebra before they had computers (No! Was there ever such a time?) I wanted to suggest that you learn to do these by hand and not rely on the graphing calculator.

But then I thought ... is that true? If someone is learning algebra today, should they learn to make a two-column table, label the columns x and f(x), and plug in numbers by hand? Then plot the points (x, f(x)) on graph paper. This is how you get a visceral feel for the functions.

But I do wonder if that's true. I'd love to hear people's opinions about this. When we teach algebra in the modern world, should we make people graph points by hand and only use the calculator as a secondary tool? Or should i just forget about it, get off my dinosaur, and tell the kids, 'There's an app for that!"

OP what do you think? Do you understand that the points on the graph are exactly the points (x, f(x)) on the plane? That's the main thing to know.
I think the whole mathematical curriculum needs to be revised based on the new tools available.

I still have sitting on my desk Standard Mathematical Tables. I remember when using logarithms was an essential of computations. I know how to use a slide rule, but I think mine is lost.

I'd like to see far more reliance on electronic tools in place of mechanical drills and a huge increase in word problems so that students get more experience in deciphering what tools apply to different situations.

The main advantage to graph sketching, which really requires differential calculus is that are sure to understand why the graph looks as it does. So I would not eliminate skills such as graph sketching, but I sure would place far less emphasis on it.
JeffM1 is offline  
March 21st, 2017, 06:56 PM   #9
Member
 
Joined: Jan 2017
From: US

Posts: 65
Thanks: 5

Quote:
Originally Posted by Maschke View Post
As an oldtimer who learned algebra before they had computers (No! Was there ever such a time?) I wanted to suggest that you learn to do these by hand and not rely on the graphing calculator.

But then I thought ... is that true? If someone is learning algebra today, should they learn to make a two-column table, label the columns x and f(x), and plug in numbers by hand? Then plot the points (x, f(x)) on graph paper. This is how you get a visceral feel for the functions.

But I do wonder if that's true. I'd love to hear people's opinions about this. When we teach algebra in the modern world, should we make people graph points by hand and only use the calculator as a secondary tool? Or should i just forget about it, get off my dinosaur, and tell the kids, 'There's an app for that!"

OP what do you think? Do you understand that the points on the graph are exactly the points (x, f(x)) on the plane? That's the main thing to know.
Maschke,

I definitely understand what you're saying, and here's my honest opinion:

I think learning to do things without electronic reliance is usually very important, and that trusting your own brain more so than a calculator is a smarter option. I think technology can be a great thing, though maybe we could be using it in some other ways. In general, I don't think the whole "there's an app for that!" stance will get you very far. I also think it's good if you can learn to think for yourself, with some common sense, rather than relying on technology.


However, here's my predicament with this: I don't know where you live, but in the US, Common Core is pretty out of hand- with math particularly. It isn't about simply solving a problem like a+b anymore- you have to go through a set of nonsensical steps (because, you can't just use your brain and add), along with about an essay of a description of why you did what you did, or else you don't points at all (even if your initial answer was correct). And, might I add, the steps they are making everyone go through make no sense, and will never need to be used by anyone in life (unless you become a common core professor or something). In that case, I don't think calculators are such a bad thing, as long as you know how to do the basic math that you will actually use in life.


As a student who has been dealing with common core for a while, and can actually think for herself, that is my humble opinion. However, I can definitely see where you're coming from.

Last edited by Indigo28; March 21st, 2017 at 07:00 PM.
Indigo28 is offline  
March 21st, 2017, 07:15 PM   #10
Senior Member
 
Joined: Feb 2016
From: Australia

Posts: 982
Thanks: 347

Math Focus: Yet to find out.
Quote:
Originally Posted by Maschke View Post
As an oldtimer who learned algebra before they had computers (No! Was there ever such a time?) I wanted to suggest that you learn to do these by hand and not rely on the graphing calculator.

But then I thought ... is that true? If someone is learning algebra today, should they learn to make a two-column table, label the columns x and f(x), and plug in numbers by hand? Then plot the points (x, f(x)) on graph paper. This is how you get a visceral feel for the functions.

But I do wonder if that's true. I'd love to hear people's opinions about this. When we teach algebra in the modern world, should we make people graph points by hand and only use the calculator as a secondary tool?
It's an interesting point for sure. I think the problem is, trying to remember a time when you didn't know how to actually plot a graph. Even in a general sense.

I can't... So I can't say for sure what it would have been like to have skipped doing that by hand and instead used software to plot graphs.

Last edited by skipjack; March 22nd, 2017 at 12:17 PM.
Joppy is offline  
Reply

  My Math Forum > High School Math Forum > Algebra

Tags
algebra, andwhat, functions, graphing



Thread Tools
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Algebra graphing question Manu Baber Algebra 4 October 11th, 2016 10:52 AM
Need Help Graphing 2 Trig Functions JBake010 Trigonometry 1 March 11th, 2012 03:14 PM
Graphing functions in a Domain Ndjs Algebra 2 April 4th, 2011 09:20 PM
Graphing Functions Nexusfactor Algebra 1 November 29th, 2010 01:53 PM





Copyright © 2017 My Math Forum. All rights reserved.